Investigation of Laser Surface Texturing and Injection Molding Parameters in Advanced High-Strength Steel-Polyamide Direct Joining

This study investigates the joining of dissimilar materials, specifically galvannealed advanced high-strength steel (AHSS) and glass fiber-reinforced polyamide 6 (PA 6) to achieve lightweight automotive. AHSS and PA 6 are widely used in the automobile industry; however, a direct joining of those two materials is difficult owing to their great difference in physical properties. Therefore, laser surface texturing (LST) and plastic injection molding are adopted to join AHSS and PA 6, which can create a strong mechanical interlock between AHSS and PA 6, resulting in an excellent joint strength compared to other joining techniques. The effects of LST parameters (groove depth and hatch distance) and injection molding temperatures on the joint strength are examined. The maximum AHSS-PA 6 joint strength is measured at 72.3 MPa. Additionally, the microstructure and mechanical properties of recast, which develops over the original metal surface by melting and resolidifying, are analyzed. Compared to the base metal, the recasts exhibit higher hardness due to smaller grain sizes. PA 6 fills the laser-textured grooves and spaces between the recasts, acting as a mechanical interlock that enhances joint strength under tensile shear testing.